Yamaha gear is very good value for money, so no prob there.
One point of note is that if you buy a powered mixer you will find it more difficult to 'upgrade'; sep' amp and mixer means you can upgrade either as and when. Don't forget to look at powered speakers and a passive (no in built power amp) desk.
Go for the most power, greatest no. inputs, largest speaker you can (assuming you are looking at same spec/quality speakers... top quality small speaker will be better than poor large dia driver).
Are you going to buy new or used? If you have the cash for used, you'll get loads more for your money. I'm not plugging BUT if you wanted a starter package to see how it goes, I have a 12 channel mixer (built in effects) and 900w power amp (450w per side into 4 ohms) you could start with for about the same money you'd pay to hire a PA for ONE pub gig (just add your own speakers).
Good luck either way.